Field of the Invention
The invention relates to a surface-mountable light-emitting diode light source. In the surface-mountable light-emitting diode light source, a LED chip is mounted on a leadframe and the leadframe is encapsulated with a one-piece transparent plastic molded body. A leadframe connection for the LED chip protrudes from the transparent plastic molded body on each of at least two side faces.
The invention also relates to a method of producing a light source on the basis of a semiconductor light-emitting diode (hereafter referred to as semiconductor LED), in particular a surface-mountable semiconductor LED. It further relates to producing a semiconductor LED mixed-light source, in particular a white-light source.
A surface-mountable LED component with solder connection parts protruding from the package is described in International PCT publication WO 98/12757. In that device, the solder connection strips of a leadframe, extending from the chip mounting surface in a straight line in the plane of the mounting surface, are led out from a plastic package. When outside the plastic package, the solder connection strips are bent toward the component mounting side in an S-shaped manner, so that solder connection areas are produced after the S bend. With the solder connection surfaces, the component can be mounted on a printed circuit board.
WO 98/12757 also describes a wavelength-converting molding composition for an electroluminescent component with a body emitting ultraviolet, blue or green light on the basis of a transparent epoxy resin that is mixed with a luminescent substance (in particular, with an inorganic luminescent pigment powder with luminescent pigments from the group of phosphors). A white-light source is described as a preferred embodiment in which a radiation-emitting semiconductor LED on the basis of GaAlN with an emission maximum between 420 nm and 460 nm is used together with a luminescent substance, which is chosen such that a blue radiation emitted by the semiconductor body is converted into complementary wavelength ranges (in particular blue and yellow, or to additive color triads, for example, blue, green and red). The yellow, green and red light is produced by the luminescent substances. The color tone (color locus in the chromaticity diagram) of the white light produced in this way can be varied by suitable choice of the luminescent substance or substances with regard to mixing and concentration.
Similarly, International PCT publication WO 98/54929 discloses a visible light-emitting semiconductor component with a UV/blue LED, which is disposed in a depression in a supporting body, the surface of which has a light-reflecting layer and is filled with a transparent material. The transparent material surrounds the LED on its light-exiting sides. The transparent material has a refractive index that is lower than the refractive index of the light-active region of the LED to improve the coupling out of the light.
Japansese patent application No. JP 05 037 008 discloses a surface-mountable LED component. Solder connection strips are led out on the underside of a molded plastic body from the plastic body. At the point at which they leave, the solder connection strips are bent out of the plastic body in such a way that their ends point horizontally outward in a straight line along the underside of the plastic body.
German Patent DE 196 04 492 C1 describes a radial construction of LED components. However, such a construction is not suitable for surface mounting, but only for through-hole mounting on a printed circuit board. The plastic encapsulation of the package, which substantially defines the radial construction, is made of polycarbonate.
Japansese patent Application No. JP-10093146 A describes a radial LED component. A luminescent substance excited by the radiation of the semiconductor LED chip and emitting at a relatively great wavelength is incorporated in the plastic encapsulation of the package to improve the radiation intensity and brightness.
A radial LED construction is described in U.S. Pat. No. 5,777,433 also. Nanoparticles, which have a greater refractive index than the transparent encapsulating material are incorporated in the radial plastic encapsulation to increase the refractive index of the plastics material. The radial plastic encapsulation contains, for example, epoxy or some other suitable transparent organic encapsulating material.
German patent application DE 38 04 293 discloses a white-light source on the basis of a semiconductor LED. A configuration with an electroluminescent or laser diode is described, in which the emission spectrum emitted by the diode is displaced toward greater wavelengths via an element of plastic mixed with a phosphorescent, light-converting organic dye.
As a result, the light emitted by the configuration has a different color than the light emitted by the light-emitting diode. Depending on the type of dye incorporated in the plastic, configurations of light-emitting diodes that illuminate in different colors can be produced with only one light-emitting diode.
In many potential areas of application for light-emitting diodes, for example, in the case of display elements in a motor-vehicle dashboard, illumination in aircraft and cars and in the case of full-color LED displays and in portable devices with display elements or back-lit parts (e.g., in the case of cell phones), the requirement for particularly space-saving configurations of light-emitting diodes is increasing. Corresponding LED components with which mixed-colored light, in particular white light, can be produced are required.
In the case of conventional surface-mountable constructions described above, firstly a prepackaged component is produced by encapsulating a prefabricated leadframe with a suitable plastics material, which forms the package of the component. This component has a depression, on the upper side, into which leadframe connections are inserted from two opposite sides. A semiconductor LED is adhesively attached and electrically bonded to one of the connections. Then the depression is filled with an encapsulating composition, for example, a transparent epoxy resin mixed with the luminescent substance.
The advantage of the conventional surface-mountable constructions is that a very directed emission can be achieved and the side walls formed by the plastic package can be formed as tilted reflectors. However, in the applications in which such a directed emission is not absolutely necessary, the method of production is relatively complex and contains multiple stages, since the plastic of the package and the encapsulating composition are formed by two different materials and have to be molded-on in separate method steps. Moreover, the problem of an adequate and temperature-stable bond between the encapsulating composition and the plastic of the package must always be solved. This repeatedly leads to problems in practice, in particular where high light outputs are used. Further, the extent to which miniaturization can be carried out is limited by the two-part form of the package.
The extent to which the radial constructions described above can be miniaturized is likewise greatly restricted because of the required through-hole mounting. Furthermore, with the circuit configurations nowadays generally produced by surface mounting, the through-hole mounting represents a separate mounting step that is technically different from surface mounting.